Stability of vancomycin hydrochloride employed in antimicrobial seal solutions of central intravenous catheters

Abstract Objective: to verify the stability of vancomycin hydrochloride in antimicrobial seal solutions with and without association of heparin sodium according to temperature and association time. Method: an experimental study designed for the analysis of hydrogenionic potential and concentration by means of high-efficiency liquid chromatography of vancomycin hydrochloride (n=06) and vancomycin hydrochloride and heparin sodium (n=06). The solutions studied were submitted to absence of light, as well as to 22°C and 37°C. Analyses in triplicate (n=192) were performed at the initial moment (T0) and three (T3), eight (T8) and 24 hours (T24) after preparation. The data were submitted to analysis of variance (p≤0.05). Results: concentration of the antimicrobial at 22°C presented a reduction (T0-T8) and a subsequent increase (T24); hydrogenionic potential decreased significantly over time. At 37°C, the concentration increased up to T3 and decreased at T24, with a reduction of hydrogenionic potential up to 24 hours. Concentration of the vancomycin hydrochloride and heparin sodium solutions varied with a reduction at 22°C, accompanied by increased hydrogenionic potential. Precipitate formation was observed by visual inspection of the vancomycin hydrochloride-heparin sodium association (T3). Conclusion: pharmacological stability of vancomycin hydrochloride (5 mg/mL) and physical incompatibility with heparin sodium (100 IU/mL) were evidenced after three hours of association in the antimicrobial seal solutions studied.


Introduction
Critically-ill patients often require multiple drugs, almost all of them intravenously, in order to guarantee the plasma levels in the concentration and time required for an adequate therapeutic response (1) . Consequently, the use of central intravenous catheters (CICs) has been indicated, due to the characteristics of most of the drugs employed, osmolarity and hydrogenionic potential (pH), among others (2)(3)(4) .
CIC preservation in patients with chronic diseases is essential. However, prolongation of the use time of these devices is a predisposing factor for central catheter-related bloodstream infection (CCRBSI) (5)(6) , due to biofilm formation in the lumen of the catheter (7) . The traditional intervention involves removal of the device. However, this is not always feasible for these patients due to the restricted vascular network resulting from multiple punctures and treatment, as well as from the clinical condition, factors that hinder invasive interventions or procedures.
Thus, use of the seal technique with antimicrobials in CICs emerges as an adjuvant in the treatment (2,5) .
It comprises the administration of antimicrobials with a strong recommendation for the use of vancomycin hydrochloride (5,(8)(9) in the lumen of the catheter at a concentration 100 to 1,000 times higher than the minimum inhibitory value usually employed for systemic therapy (8) , being frequently used in combination with heparin sodium (10)(11) .
The solution used in the lumen of the CIC has the function of decontamination, being a sine qua non condition for maintaining stability of the drugs within the device during the period indicated for the expected effect (8,11) .
A number of studies indicate that the antimicrobial seal may remain in the lumen of the intravenous catheter for a long period of time, in order to overcome the barrier formed by the microbial biofilm (8)(9)(11)(12) .
However, there is no evidence related to the maximum volume to be administered, permanence time of the solution in the catheter lumen, use frequency and adequate concentration, as well as the association with an anticoagulant (5,8,12) . Most clinical studies propose a minimum of eight hours a day to achieve the expected action (8)(9)12) . However, there is also the recommendation for the solution to remain between 24 and 48 hours inside the CIC (8) .
Thus, the concern about antimicrobial stability in association with heparin sodium remains. Although these phenomena are dependent, among other factors, on concentration of the drugs, exposure to higher temperatures and contact time between the medications should also be evaluated (9,(11)(12) .
Thus, the objective of this study was to verify the physical-chemical stability of vancomycin hydrochloride in antimicrobial seal solutions with and without heparin sodium according to temperature and association time.

Study design
An experimental research study, mimicking the clinical practice of antimicrobial seal administration in CICs.

Data collection period
Data collection took place between May and July 2018.

Samples
Vancomycin hydrochloride solutions in physiological serum (PhS) and in association with heparin sodium, equivalent to those employed in the antimicrobial seal technique in central intravenous catheters.

Sample definition
The sample consisted of 12 solutions, namely: three of vancomycin hydrochloride at 22°C, three of vancomycin hydrochloride at 37°C, three containing the association of antimicrobial and heparin sodium at 22°C, and three containing the association of antimicrobial and heparin sodium at 37°C. The solutions were prepared by a single researcher and the pH and concentration measurements occurred at the initial moment (T0) and at three (T3), eight (T8) and 24 hours (T24). Concentration checks were carried out in triplicates, resulting in 192 measurements (48 for pH and 144 for concentration).

Study variables
Simulating the clinical practice of antimicrobial seal administration, the experiments took place under controlled light and temperature conditions. The 37°C temperature aimed at mimicking body temperature. The drug concentrations were based on the Infectious Diseases Society of America (IDSA) Practice Guidelines (13) . Two different solutions were studied: vancomycin hydrochloride

Ethical aspects
The study was submitted to the evaluation of

Results
The results of the concentration and pH study were obtained by analyzing 12 vancomycin hydrochloride solutions and solutions containing the vancomycin hydrochloride-heparin sodium association. Table 1 shows the results of the concentration and pH study corresponding to the solutions according to time and temperature variations.
www.eerp.usp.br/rlae Rev. Latino-Am. Enfermagem 2022;30:e3621.  Under the influence of the 37°C temperature, the vancomycin hydrochloride concentration was increased at the initial moment, as well as at three hours of preparation with a subsequent decrease at 24 hours (Table 1).
Regarding pH, there was no significant variation in relation to the values found in the vancomycin hydrochloride solutions at 22°C with a reduction in the pH scale from the initial moment up to 24 hours, as shown in Table 1.
In relation to the vancomycin hydrochloride-heparin sodium association solution at 22°C, regarding pH, a lower value was observed at three hours of preparation, and a higher value at 24 hours. Regarding the concentration, it presented a drop of around 5% in the antimicrobial values over time (Table 1).
In the vancomycin hydrochloride with heparin sodium solutions, when submitted to 37 o C and with regard to pH, it is noted that they presented a higher value at T0, although with a smaller variation. As for the concentration, they presented a drop at the initial moment, reaching their maximum concentration 24 hours after preparation of the solutions (Table 1).
To graphically show the variation in concentration and pH obtained in the study, the results, according to the preparation time of the solutions, are presented in  Regarding the analysis of antimicrobial pH at both temperatures, it was observed that the values remained similar, except for 24 hours at 22°C, which proved to be more acidic (Table 1) the HPLC method that revealed pharmacological stability of the antimicrobial for up to 24 hours at room temperature (17) .
However, the association of vancomycin hydrochloride with heparin sodium resulted in precipitate formation at three hours at both temperatures, as well as in reduced antimicrobial concentration when at 37°C.
It is known that the predominant profile of drug incompatibilities with potential risks for the patient is related to the class of antimicrobials, and the association between drugs may inactivate the active ingredient of the product or lead to toxicity, resulting in uncertainty of therapeutic efficacy (18)(19) . Recognition of pharmacological incompatibilities makes it possible to avoid adverse situations, as well as the emergence of toxicity (20)(21) .
To ensure the efficacy of vancomycin hydrochloride in decontamination of CICs, concentration of the drug should be maintained at a variation of less than 10% throughout the period in which the solution remains inside the intravenous device, also taking into account the materials of the CICs (22) . to the manufacturer (23) .
A study on drug stability states that extreme pH values can cause instability of the solutions and are considered key elements for physical-chemical compatibility of the solutions (24) .
Changes in the temperature to which the solutions are submitted can cause pH changes and consequent pharmacological instability (18,21,25) . However, in this  Solutions of vancomycin hydrochloride isolated or associated with heparin sodium were identified as the best alternatives for the treatment of CCRBSIs for Grampositive microorganisms (26)(27) . However, with regard to drug stability, the results were contradictory, especially for antimicrobial-heparin sodium association solutions since, although in one study (28) vancomycin hydrochloride (5 mg/ mL) was compatible with heparin sodium (2.5000 IU/ mL), others, in turn, indicated that high concentrations of antimicrobial (10 mg/mL) can increase the risk for precipitation of the solutions, even with low doses of anticoagulant (100 IU/mL) (29) .
In this study, when at 22°C, there was a reduction in the vancomycin hydrochloride concentration after the association with heparin sodium in the evaluation of the solution after 3 hours of the 2.72% preparation.
In a similar research study, a reduction in antimicrobial concentration was demonstrated in solutions containing vancomycin hydrochloride and heparin sodium inside CICs after 72 hours, suggesting, among other things, the interaction between the drugs as well as between the solutions and the intravenous device material (30) .
A study conducted in a hospital found that most of the medication errors observed were related to drug incompatibility or to lack of evidence for administration associated to the drugs (31) . Drug incompatibility occurs when two or more drugs react or interact in a way that there is a change in the normal activity of one or more components, a fact that can derail clinical therapy, resulting in alteration of the active ingredient, precipitation or clouding of the solution and change in the color of the drug (20)(21)32) .
A research on study vancomycin hydrochloride stability showed precipitate formation and turbidity when in association with heparin sodium from five minutes of solution preparation (29) . In the current study, changes were Feasibility of the occurrence of drug incompatibility and the scarcity of scientific evidence are difficulties found in nurses' daily practice. It is to be remembered that performing drug associations without scientific evidence incurs in medication errors (33)(34) . under the possible interference of the material of intravenous devices and at a concentration of 10 mg/mL.

Conclusion
There was a change in physical stability in the vancomycin hydrochloride (5 mg/mL) and heparin sodium (100 I.U./mL) solution at three hours of association with a reduction of less than 10% in antimicrobial concentration, evidencing chemical instability with drug degradation, although with pharmacological stability.
The vancomycin hydrochloride solutions maintained at 22°C presented the smallest variations in pH. However, temperature does not seem to be an environmental factor triggering considerable differences in the chemical behavior of the solutions studied.
Thus, this study evidenced that, regardless of temperature, the association of vancomycin hydrochloride with heparin sodium in solutions used in seals for CIC decontamination presented chemical instability and drug incompatibility. Despite maintenance of pharmacological stability, it is therefore recommended to adopt non-use of these compounds in association in the seal technique with an antimicrobial.

Acknowledgments
We thank the members of the SEGTEC -Segurança e Tecnologia Research Group -Nursing research study group on patient safety, intensive care and intravenous therapy in pediatrics (Brazil) for their support during data collection.
To the team of the Laboratory of Nursing Experiments (LEEnf).